A LED array is the main power consumption part of an outdoor LED display panel having a large display area and high power consumption. Therefore, there exists the need to enhance the luminous efficiency of a LED array so as to reduce the power consumption of the outdoor LED display panel.
The luminous efficiency of a LED array is mainly dependent on LED drive modes. The common modes of LED drive can be roughly classified into two categories: analog or direct current (DC) and switch pulse width modulation (PWM). When using either analog or direct current (DC) drive modes, a LED array has the highest luminous efficiency and the optimal color stability. However, the illumination output of a LED array varies nonlinearly, so that it is unable to dim linearly, which makes the lighting output unstable. When using the switch pulse width modulation mode, two direct currents are periodically switched to supply the LED. One of the direct currents is zero, commonly referred to as the low level direct current, and the other direct current is greater than zero, commonly referred to as the high level DC current. By adjusting the duration of the high level direct current, the effective value of the power supply current can be adjusted, and then the illumination output of a LED is adjusted. However, this kind of drive mode causes the luminous efficiency of a LED to be reduced.